vk-pause

There are pre-defined constants corresponding to usually non-typable
keys on the keyboard (see key-names). When a Lisp function
calls for a virtual key argument, one of the pre-defined constants is
suitable as an argument value. The word after the hyphen names the
key, in this case the Pause key. See also vk-cancel, as that keycode is used when
Pause/Break is pressed while either of the two control keys is held
down.